Apparatus for atomizing oil



Oct. 10, 1967 A. BIBER ETAL APPARATUS FOR ATOMZING OIL 4 Sheets -Sheet lFiled Dec. 5, 1964 wywro s. BRUCE R. WALSH e ALBERT BIBER 1967 I A.BIBER.ETAL I 3,346, 96

APPARATUS FOR ATOMIZING OIL ALBERT BIBER Oct. 10, 1967 Filed Dec. 5,1964 A. BBE ETAL APPARATUS ;FOR ATOMIZING OIL 4 Sheets-Sheet 5/IVVENTO/? BRUCE R. WALSH ALBERT BlBER Oct. 10, 1967 A. BIER ETALAFPARATUS FOR ATOMIZING OI L 4 Sheets-Sheet 4 Filed Dec; 5, 1964 3 5 C 4fil B AL D .M I//O/ 1 I H 0 5 4 3 2 o mmm 532 %Dum mxom PERCENT CAR BOND\ OX I DE PERCENT CARBON DIOXIDE Fig. 7

PERCENT CARBON D)OX I DE PERCENT CARBON moxDE Fig VVENTOPS. BRUCE R.wALsH ALBERT. BIBER United States Patent O 3,346,196 APPARATUS FORATOMIZING OIL Albert Biber, Verona, and Bruce R. Walsh, Pittsburgh,

Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa.,a Corporation of Delaware Filed Dec. 3, 1964, Ser. No. 415,720 Clams.(Cl. 239-404) The invention relates to an apparatus and process for thecombustion of fuel oil at a substantially optimum level of combustionefficiency.

An optimum in efiiciency for any combustion operation is the attainmentof substantially complete combustion of the fuel in the presence of onlyabout the theoretically required amount of air, with substantially noexcess air being present. This optimum in combustion eiciency isexceedingly difiicult to attain. Complete combustion is rarely achievedin a burner unless a substantial quantity of excess air is admitted.However, excess air in a combustion operation is disadvantageous becausethe excess air constitutes a diluent in the combustion product gases anddecreases the temperature of these gases, thereby decreasng the heatexchange potential of the system. Furthermore, passage of excess airthrough a combustion apparatus decreases the residence time of the hotcombustion product gases in a heat exchange system to which thecombustion gases are charged. These are the two primary disadvantages ofadmittng excess air to a combustion apparatus. While it is extremelyrare in an oil burner apparatus that complete combustion is achievedunless a substantial amount of excess air is admitted, the oil burnerapparatus and process of this invention achieves the unusual eificiencylevel of substantially complete combustion of fuel in the presence ofonly about a stoichiometeric quantity of air.

The oil burner apparatus of this invention comprises a plurality ofparts Operating interdependently. The apparatus includes an aspiratingnozzle disposed axially within an air blast tube close to or at thedischarge opening of the air blast tube. Fuel oil under atmosphericpressure is exposed to said nozzle from a level which is the same as orsomewhat below the level of the nozzle. The aspirating nozzle is adaptedso that a swirling stream of compressed air passing therethrough drawsthe fuel oil into the nozzle where the oil becomes involved in theswirling motion of the compressed air stream and the resulting mixtureis sprayed from the nozzle as a swirling diverging mixture of compressedair and highly atomized fuel oil droplets. An air choke having air swirlvanes is disposed at the discharge end of the air blast tube andsurrounds the aspirating nozzle. An axial air disk having a diametersmaller than the diameter of the air blast tube is disposed within theair blast tube upstream from the nozzle. An air blower is disposedupstream from the air disk and blows atmosphen'e air through the annularspace between the air disk and the air blast tube to form a hollowcylindrical stream of air directed toward the vaned air choke. The vanedair choke imparts a swirling con- Vergent flow pattern to the air. Theair blower blows atmospherc air through the air tube without causing anysignificant pressure within the tube.

The compressor employed to supply compressed air for the aspiratingnozzle is capable of delivering air at a pressure considerably higherthan that deliverable by the air blower. For example, the nozzle aircompressor can be adapted to deliver air at a pressure above about 1 andup to about pounds per square inch. A nozzle air pressure between about2 and S pounds per square inch is usually sufficient. The compressed airis swirled within the aspirating nozzle and forms an evacuated vortexinto which fuel oil under atmospheric pressure is aspirated.

3,346,196 Patented Oct. 10, 1967 The oil aspirated into the nozzlebecomes engulfed in the swirling stream of compressed air and is flungoutwardly against the nozzle swirl chamber wall surface under theinfluence of centrifugal force where it swirls as a thin liquid film.The swirling oil is carried out of the nozzle 'by the swirling stream ofcompressed air and, upon release from the confines of the nozzle, thethin oil film being still under the influence of centrifugal forcediverges and disintegrates to form a divergent spray comprsing highlyatomized fuel oil droplets Suspended in compressed air. Concomitantly,the vaned air choke directs the air being blown through the air blasttube in a swirling converging path directly intercepting the nozzlespray. An intimate admixture results comprsng swirling atmospheric airfrom the air blower and unpressurzed highly atomized droplets of fueloil Suspended in swirling expanding air from the air compressor.

The use of a swirling aspirating nozzle as described is highly criticalto the attainment of substantially complete combustion of fuel oil inthe presence of only approximately a stoichiometric quantity of air. Itwas found, and illustrated in Example 4, below, that if fuel oil ispumped under pressure through a swirling spray nozzle the highlyadvantageous combustion performance of this invention is not achieved.While the atomized fuel oil droplets in the spray of an aspiratingnozzle are passively suspended in a carrier stream of compressed air andremain there until burned, a radically different condition prevails inthe spray from a nozzle to which oil is pumped under pressure. When oilis pumped under pressure through a nozzle, rather than aspirated, thedischarge fuel oil droplets are not passively Suspended in a carrier airstream, as in the case of an aspirating nozzle, but are impelled fromthe spray nozzle under their own momentum and can impinge upon the wallsof a surrounding combustion chamber and wet those walls with oil beforethey can be substantially completely vaporized and burned.

It was also found, and illustrated in Example 5, below, that if fuel oilis aspirated under atmospheric pressure by means of compressed air, butthe nozzle employed is not equipped with means for swirling theaspirated oil, the extremely high level of combustion efficency of thisinvention is not achieved. The reason evidently is that a high degree offuel atomization is not achievable in the absence of swirling. When aswirling film of oil is released from the confines of a nozzle swirlchamber wall surface centrifugal force causes it to suddenly divergelaterally and disintegrate into a highly atomized mist of oil droplets.A high degree of oil atomization encourages rapid and completevaporization of individual oil droplets. It is only in the vapor statethat oil can admix with sufiicient air to support its combustion. It isnoted that oil vapor is highly combustible because it freely adrnixeswith air while oil in the liquid state is not combustible because aliquid cannot admix With sufficient air to support combustion.Therefore, a liquid oil droplet only burns at its surface wherevaporization can occur, but the liquid nucleus of the droplet will notburn unless it can first vaporize. It is critical to the attainment ofthe highly superior combustion performance of this invention both thatthe fuel oil be swirled and sprayed as a mist of highly atomizeddroplets which will rapidly and completely vaporize and also that thehighly atomized oil be suspended in a carrier stream of expandingcompressed aspirating air which air will advantageously be present toadmix with the oil immediately upon vaporization thereof.

As explained above, the combustion apparatus and process of thisinvention achieves substantially complete combustion of fuel oil in thepresence of only approxi mately a stoichiometric quantity of air. It hasbeen discovered in accordance with this invention, that in order toachieve this high level of combustion efliciency a portion of thestochiometric quantity of air must be compressed air, as contrasted toatmospheric air which is blown through the air blast tube. The pressureof atmospheric air blown through an air blast tube is only high enoughto impel atmospheric air through the air blast tube and is well under 1pound per square inch, rarely reaching 1 to 3 ounces per square inch,and often being close to zero ounces per square inch. On the other hand,the compressed air utilized in accordance with this invention is under amuch higher pressure. The compressed air can be under a pressure ot fromabove about 1 up to about 10 pounds per square inch, generally, and ispreferably under a pressure of about 2 to 6 pounds per square inch.

A minimum critical rato of compressed air to fuel oil must be utilizedin order to attain substantially complete combustion of the fuel oilwithout appreciable excess air. This is illustrated in Examples 1 and 7,below. The minimum critical rato can be as low 'as about 70 or 75, andis preferably about 90 to 120 cubic feet of compressed air under apressure of above about 1 up to about 10 pounds per square inch for eachgallon fuel oil. This rato can vary depending upon many differentfactors `such as the pressure of the compressed air, the composition ofthe fuel oil, the degree of oil atomization achieved by the aspiratingnozzle, and the relative dimensions of the various Components of thecombustion apparatus, However, in each combustion apparatus and processof this invention, a portion and only a portion of the combustion air iscompressed air, the remainder of the stoichiometrically required airbeing blown through the system at or very close to 'atmosphericpressure. Example 6, below, shows that there is no advantage inincreasing the rato of compressed air to fuel oil above the minimum ratorequired for optimum combustion performance. The proportion of thecombustion air which must be introduced under compression is a minorproportion of the stoichiometric air requirement, with the majorproportion of the stoichiometric air requirement being blown through thesystem 'at or close to atmospheric pressure. For example, in certaincombustion Operations of this invention, between about and percent ofthe stoichiometrically required air must be introduced undercompression, the remainder being introduced under about atmosphericpressure. There is generally no advantage in exceeding the criticalminimum proportion of compressed air required to achieve substantiallycomplete combustion with only a stoichiometric quantity of total Sincethe aspirating nozzle of this invention utilizes pressurized air for itsoperation, it is advantageous to utilize an aspirating nozzle having anOperating rato of compressed air to aspirated oil such that the totalrequired quantity of compressed air can be introduced into the apparatusof this invention via the aspirating nozzle. Example 7, below,illustrates an advantageous means for increasing the rato of compressedair to fuel oil discharged from a nozzle. This means comprisesincreasing the vertical distance between the fuel oil supply reservoirand the aspirating nozzle to increase the height through which theaspirated fuel oil must be lifted. However, many aspirating nozzles 'areoperative only at a rato of compressed air to aspirated oil which is toolow to satisfy the critical minimum compressed air requirements of thisinvention. In many aspirating nozzles, an attempt to increase the amountof compressed air passed through the nozzle above a critical levelresults in a velocity at the nozzle discharge orifice which is so highthat it exceeds the velocity of flame propagation, whereby either thenozzle spray cannot be ignited or the flame is repeatedly extinguished.In these instances it is necessary to introduce the additionallyrequired compressed air directly into the air blast tube. When theaspirating nozzle is unable to supply the total required quantity ofcompressed air and additional compressed air must be introduced directlyinto the air blast tube, the additional compressed air is introducedinto the air blast tube at a position on the periphery of said tubeimmediately Upstream from the vaned air choke and is directed toward theswirling vanes of the air choke. Introduction of compressed air at thislocation permits the vaned air choke to impart a swirling convergentflow pattern to the expanding compressed air, thereby furtheringintermixing of the compressed air stream and the separate but closelyproximate divergent spray from the aspirating nozzle which is enclosedand intercepted by it.

compressed air can be advanta-geously introduced directly into the airblast tu'be via a hollow ring having air inlet means and having airdischarge openings directed toward the air swirl vanes on the air choke.If compressed air is charged to the air tube, it must enter the air tubeclose to and upstream from the air swirl vanes on the air choke so thatthe compressed air is swirled by said vanes if the superior combustionperformance of this invention is to be achieved. This is illustrated inExample 2, below. Combustion tests showed t-hat highly inferior resultsare achieved when the compressed air is charged at the downstream end ofthe air swirl vanes or upstream from the air swirl vanes but close tothe aXis of the air tube, in both of which instances the air swirl vanesbeing unable to swirl the compressed air admtted tothe air tube. Ofcourse, when the entire required quantity of compressed air is chargedthrough the nozzle, the nozzle imparts a swirling motion to said air.

Regardless of whether the total required quantity of compressed air isintroduced through the aspirating nozzle or is introduced partiallythrough the aspirating nozzle and partially directly into the air blasttube, the vaned air choke is a critical Component of the apparatus ofthis invention. This is illustrated in Example 2, below. The majorportion of the stoichiometrically required air flows through the airblast tube and not through the nozzle. If complete combustion is to -beac-hieved in the absence of excess air, substantially all the airflowing in the air blast tube must admix intimately with the spray fromthe aspirating nozzle. This intimate admixture is largely accomplishedby means of the vaned air choke which, in cooperation With the air disk,imparts to the air flowing in the air blast tube a convergent swirlingflow .pattern and causes this air stream to enclose and intercept thediverging swirling spray from the aspiratin-g nozzle. Intmate a-dmixtureoccurs as a result of the intersection of the convergent swirling airstream from the vaned air choke and the divergent swirling spray fromthe aspirating nozzle.

This invention will be more clearly understood by reference to theaocompanying drawings in which- FIGURE '1 schematically shows the oilburner apparatus of this invention together with a furnace-heat ex-Changer combination,

FIGURE 2 is a sectional side View of the burner a-pparatus,

FIGURE 3 is a sectional top view of the burner apparatus,

FIGURE 4 is a front view of the air choke of the burner apparatus,

FIGURE 5 is a sectional side view of an aspirating nozzle of the burnerapparatus, and

FIGURES 6, 7, 8 and 9 are curves representing data taken to illustratethe exceptional combustion performance of the apparatus of thisinvention and the criticalty of various structural componets of theburner apparatus of this invention.

A schematic representation of the oil burner apparatus of this inventiontogether with a furnace-heat exchan-ger combination is shown inFIGURE 1. The oil burner assembly is indicated generally at 10, thefurnace is indicated generally at 12, and the heat exchanger isindicated generally at 14. The flame from oil burner assembly 10 ischarged to combustion chamber 16 which has an overhead opening leadingto heat exchange chamber 18 whereby hot combustion product gases risefrom combustion charnber 16 to heat exchange chamber 18. A fluid to beheated is circulated in an enclosed conduit 19 which passes throughexchange chamber 18. Conduit 19 is advantageously an air duct of aforced air heating system which extends to heat exchange chamber 18 froman air blower. The hot combustion product gases lose -heat to conduit 19in heat exchange chamber 18 and leave the furnace through chamber 20 ina reiatively cool condition. The gases are then vented through a flue-pipe 22 which is provided with adjustable damper 24.

Reference is now made to the side sectional view of oil burner assemblyshown in FIGURE 2 and the top sectional view of oil burner assembly 10shown in FIGURE 3. As shown in FIGURES 2 and 3, air blast tube 28 of oilburner assernbly 10 extends through a furnace wall 26. Air blast tube 28is secured into the discharge opening of air blower housing 30. Motor 32is disposed on one side of air blower housing 30 while air compressor 36is disposed on the other side of air blower housing 30. Motor 32 drivesbot-h blower 34 and air compressor 36 by means of rotating shaft 38.Rotating shaft 38 is` connected to blower 34 'by means of rotatablecircular plate 41, shown in FIGURE 3. Blower 34 draws air from theatmosphere through air openings 42 in stationary circular plate 40 andblows it through air blast tube 28. Disk 44 in air blast tube 28 'has adiameter slightly smaller than the diameter of air tube 28, therebyforcing the air blowing in air blast tube 28 to be confined close to thewall of the air blast tube so that when the air reaches air choke 46disposed at the discharge end of the air blast tube a swirling motion isimparted to it by means of vanes 48 attached to the interier of airchoke 46. The amount of air blown through air tube 28 is adjusted byvarying the size of air openings 42 to provide substantially astoichometrc total quantity of air to the burner. The adjustment inblower air flow rate is accomplished by means of air opening coverplates 50 which are provided with narrow longitudinal slots 52 to permitmovement of said cover plate relative to 'bolt and nut assembly 54 andair openings 42. Cover plates 50 can be Secured at any desired positionwith respect to air openings 42 by loosening bolt and nut assem-bly 54,moving cover plate 50, and then retightening bolt and nut assembly 54.

Aspirating nozzle 54 is disposed coaxially with respect to air blasttube 28 very close to or substantially at the discharge end thereof andsubstantially in the center of air choke 46. Air compressor 36 suppliescompressed air to aspirating nozzle 54. Air compressor 36 draws air fromthe atmosphere through filter-muflier 56 and pipe 58 and dischargescompressed air to aspirating nozzle 54 through pipe 60, pressureregulator 62, pipe 64, throttle valve 66, and pipe 68. Pressureregulator 62 is adapted to discharge air at any pressure within a rangeof above a-bout l to about 10 pounds per square nch. Excess compressedair can be vented through pipe and valve assembly 59.

If, during burner operation, an increased compressed air-fuel oil ratiois required to produce optimum combustion performance and aspiratingnozzle 54 is not capable of -accepting additional compressed air Withoutthe flame being blown out, the apparatus is adapted so that compressedair is supplied directly to air choke 46. Compressed :air is supplied toair choke 46 through pipe 70, throttle valve 72, and .pipe 74 whichleads directly into -continuous hollow ring 76 within the body of airchoke 46. compressed air within hollow ring 76 is discharged through aplurality of openings 78. Referring to FIGURE 4, which shows a frontView of air choke 46, it is seen that each air opening 78 is associatedwith an air swirl vane 48 so that compressed air discharged from hollowring 76 has a swirlng motion imparted to it. Air choke 46 with thecooperation of air disk 44 thereby causes both the atmospheric air blownthrough air blast tube 28 by air blower 34 and the compressed air fromhollow ring 76 to be discharged through discharge opening '80 of the airchoke as a substantially hollow swirling converging stream of airdisposed to intercept and admix intirnately With the swirling divergingsubstantially hollow stream of compressed air and atomized oil dropletsdischarged from asprating nozzle 54.

A sectional view of aspirating nozzle 54 is shown in FIGURE 5. Thenozzle comprises a body 82 which is secured to compressed air line 68 influid tight engagement therewith. Nozzle body 82 is provided with aforward cylindrical axial discharge opening 84. Plug 86 is secured intothe interior of nozzle body 82 in fluid tight engagement with respect tosaid nozzle body. Plug 86 s provided with a forward axial duct 88 havingan outer diameter smaller than nozzle discharge opening 84 and extendingcoaxially a portion of the distance into nozzle dscharge opening 84.Axial bore 100 extends through duct 88 until it meets lateral bore 90.When plug 86 is Secured tightly into nozzle body 82, lateral bore 90 isin augnment with lateral bore 92 in nozzle body 82. An oil conduit 94extends from bore 92 in fluid tight engagement therewith. Plug 86 isalso provided with one or more peripheral slots 96 which enter swirlchamber 98 in a tangential manner. compressed air from conduit 68 entersswirl chamber 98 in a forward and tangential direction throughtangential slots 96 and swirls within swirl chamber 98 toward dischargeopening 84. The swirling moton of the air stream in nozzle dischargeopening 84 creates an evacuated vortex into which fuel oil is drawnthrough pipe 94, bores 92, 90, and 100. The aspirated o l s caught up inthe swirling air stream and a swirlng dvergng spray of compressed airand atomized oil droplets is discharged from nozzle discharge opening84. As shown in FIGURES 2 and 3, nozzle 54 is disposed substantially atthe center of air choke 46 so that the swirling converging stream of airfrom air choke 46 and the swirlng dverging stream of ar and atomized oildroplets from nozzle 54 intercept each other and intimately admix n theregion of choke discharge opening 80.

FIGURE 2 shows that oil line 94 extendng from asprating nozzle 54 iscoupled to fuel supply line which n turn provides access to oilreservoir 102. Reservoir 102 s at or slightly below the level of nozzle54 and is maintained at atmospheric pressure by means of vent 104. Pump106 supplies fuel oil to reservoir 102 through line 108. The level ofoil within reservoir 102 is adjusted by means of a plurality of overflowconduits 110, 112, 114 and 116, provided with overfiow valves 118, 120,122 and 124, respectively. Overflow conduits 110, 112, 114 and 116discharge into a common header, not shown, which can return the oil toan oil storage tank, not shown. The level of oil in the tank can only beas high as the level of the lowest overflow valve which is open. The oilsuction lift to aspirating nozzle 54 is adjusted by selectively openingany of valves 118, 120, 122 or 124 and closing any valve disposed belowthe open valve. Varying the oil lift to aspirating nozzle 54 is a meansfor effecting a desired change in the ratio of compressed air to fueloil discharged by aspirating nozzle 54.

The mixture of atomized oil droplets, compressed air and atmospheric-air at air choke discharge opening 80 is ignited by means of a pair of`arcing electrodes 128 and 130 which have connection with a powertransformer 132. The electrodes, as well as compressed air conduit 68and oil conduit 95 extend through air disk 44 and are suspended withinthe interior of 'air blast tube 28 by means of a plurality of springsupports 134.

Example J A pair of tests were conducted to illustrate the criticalityof the ratio of compressed air to fuel oil in the apparatus of thedrawings. The apparatus utilized in each test comprised an air blasttube four inches in diameter having an air blower at its inlet end andan air choke having swirl vanes at its discharge end which reduced itsdischarge opening to two inches. A swirling aspiratin nozzle wasdisposed coaxially within the air blast tube with its discharge openingof an inch upstream from the discharge opening of the choke. The nozzlewas connected to an oil reservoir under atmospheric pressure whose oillevel was one inch 'below the nozzle. An air disk 3 /2 or 3% inches indiameter was disposed in the air blast tube upstream from the nozzle.The air blast tube was directed into a `f-urnace having an overheadflue.

The nozzle air compressor in each test produced 180 cubic feet of airper hour at a pressure of 5.3 pounds per square inch, of which only 48cubic feet per hour was swirled through the aspirating nozzle. In eachtest, the 48 cubic feet per hour of air swirled through the nozzleaspirated 0.80 gallon per hour of oil through the nozzle. In the firsttest no air ring was utilized in the air blast tube and the excess 132cubic feet per hour of compressed air produced by the compressor wasvented to the atmosphere. However, in the second test an air ring wasutilized in the air blast tube immediately upstream from the. vaned airchoke, and the excess 132 cubic feet per hour of compressed air producedby the compressor not swirled through nozzle was charged to the air ringfrom which it was discharged in the direction of the vanes of the airchoke. The air ring used comprised a %i inch tube bent to form acontinuous ring having a four inch outer diameter and a 3 /2 inch innerdiameter.

The only difference between the first and second tests is that thesecond test utilized the compressed air ring while the first test didnot. The results of the first and second tests are illustrated in FIGURE6 as a graph of smoke spot number versus percent carbon dioxide in thefiue gas discharging through the stack of the furnace. In each test, anumber of smoke spot number versus percent carbon dioxide readings wereobtained by varying the amount of atmospheric air blown through the airblast tube. The results of the first test, which omitted the compressedair ring, are illustrated in curve A of FIGURE 6, while the results ofthe second test, which utilized the compressed air ring, are illustratedin curve B of FIG- URE 6.

The test data of smoke spot number versus percent carbon dioxide in asample of ue gas produced during combustion was taken in accordance withthe method described in ASTM Standards on Petroleum Products, 1960,'page 1041. For purposes of analyzing the test results, it is noted thatbest combustion results are indicated by the combination of a highcarbon dioxide content, indicating a high degree of combustion, and alow smoke content, which also indicates a high degree of combustion.While the percent of carbon dioxide can be increased by reduction of airinput, this -will have the adverse efiect of increasing smoke content.On the other hand, smoke content can be decreased by merely admitting alarge excess of air but this will have the adverse efect of greatlydiminishing the relative content of carbon dioxide. Optimum results areachieved with the combination of relatively high carbon dioxide contentand relatively low smoke content.

As explained above, an optimum in performance for any combustionapparatus is the -attainment of substantially complete combustion of thefuel while admitting only about the exact amount of air theoreticallyrequired for complete combustion, with essentially no excess air beingpresent. While this optimum in combustion performance is exceedinglydiflicult to attain and it is extremely rare that complete combustion isachieved unless excess air is admitted, it is shown below that theapparatus of this invention achieves the unusual result of substantiallycomplete combustion `of fuel in the presence of approximately only astoichiometric quantity of air.

Calculations based upon the particular fuel oil used in all the tests ofthis application showed that a carbon dioxide content in the flue gasesof 15.6 percent when there is little or no smoke theoretically indicatescomplete combustion of the fuel in the presence of exactly astoichiometric quantity of air. The calculations also showed that 1389cubic feet of air is stoichiometrically required for complete combustionof each gallon of the particular fue] oil used in all the tests. In bothtests of this example, the air compressor supplied only a smallproportion the theoretical air required for complete combustion of thefuel, the remainder being atmos-pheric air supplied by the ajr blower.In the first test of this example, the air compressor supplied 48 cubicfeet of pressurized air per hour to the nozzle to aspirate 0.80 gallonper hour of fuel oil and this was the total supply of compressed air tothe system so that the air blower would have been required to supplyabout 1063 cubic feet per hour of atmospheric air to completestoichiometric air requirements. In the second test of this example, theair compressor supplied 48 cubic feet per hour through the nozzle toaspirate 0.80 gallon per hour of fuel oil, and also supplied 132 cubicfeet per hour of compressed air through the compressed air ring, so thatthe air blower would have been required to supply about 931 cubic feetper hour of atmospheric air to complete stoichiometric air requirements.

Curve A of FIGURE 6 shows that tests made without a pressurized air ringand with a ratio of compressed air to fuel oil of 60 cubic feet ofcompressed air -per gallon of fuel oil resulted in a flue gas havingonly 11.5 percent carbon dioxide at a smoke spot number of 1. Curve B ofFIGURE 6 shows that tests made With a pressurized air ring and with atotal ratio of compressed air to fuel oil of 225 cubic feet ofcompressed air per gallon of fuel oil advantageously increased thepercentage of carbon dioxide in the fiue gas to 15.0 at a smoke spotnumber of 1. The comparison between curves A and B of FIGURE 6 showsthat a remarkable improvement in combustion is achieved at the higherratio of compressed air to fuel oil made possible by the use of thepressurized air ring. The percentage of carbon dioxide in the ue gas ata smoke spot number of l at the higher ratio of compressed air to fueloil is in the vicinity of the 15 .6 carbon dioxide fiue gas percentagetheoretically indicating complete combustion of the fuel oil with noexcess air.

Example 2 Two tests were performed to illustrate the cooperatve eifectbetween the vaned air choke at the discharge end of the air blast tubeand the pressurized air ring. The first test of this example Wasperformed under the same conditions as the tests of curve B of FIGURE 6except that the air swirling vanes were removed by machining from theinterior surface of the air choke. The result of this test is shown atpoint C in FIGURE 6. The second test of this example was performed underthe same conditions as the tests 'of curve B of FIGURE 6 except that theair choke was removed entirely from the apparatus. The result of thistest is shown at point D in FIGURE 6.

Point C in FIGURE 6 shows that when utilizing a pressurized air ring theremoval of the air swirling vanes from the air choke disadvantageouslyreduced from 15 to 14 the percentage of carbon dioxide in the flue gasat a smoke spot number of 1. Point D of FIGURE 6 shows that the removalof the air choke entirely when utilizing a -pressurized air ringdisadvantageously reduced from 15 to 12 the percentage of carbon dioxidein the flue gas at a smoke spot number of 1. The tests of this exampleshow that the compressed air ring and the vaned air choke cooperate toproduce a carbon dioxide content in the ue gas at a smoke spot number of1 which is comparable to the percentage of carbon dioxide in flue gasindicating theoretically complete combustion with no excess Example 3Further tests were conducted to illustrate the interdependence betweenthe compressed air ring .and the vaned air choke. In these tests acompressed air ring was disposed snugly around the discharge end of theaspirating nozzle remote from both the wall of the air blast tube andthe air choke so that air blown by the blower through the air blast tubefiowed between the compressed air ring and the vaned choke. This iscontrasted to the tests of Examples 1 and 2 wherein the compressed -airring was disposed directly at the wall of the air blast tube upstreamfrom and adjacent to the air choke and remote from the nozzle. The testsof this example indicated that when the compressed air ring is disposeddirectly around the nozzle and remote from the air choke not only isthere no improvement in combustion but, on the contrary, there is adeleterious efiect upon combustion. These tests, therefore, illustratethe criticality of disposing the compressed air ring directly at thewall of the air blast tube immediately upstream from the vaned airchoke.

Example 4 Two tests were performed to determine the eect of thecompressed air ring in a combustion appar atus similar to that shown inthe drawings except that the aspirating nozzle s replaced by a swirlingoil spray nozzle wherein the oil is pumped under pressure through thenozzle with a swirling motion, rather than aspirated. In each of thesetests 0.87 gallon per hour of fuel oil Was pumped through a swirlingspray nozzle under a pressure of 100 pounds per square inch. In eachtest `an air choke having air swirling vanes was utilized which reducedthe discharge opening of the air blast tube from 4 inches to 2 inchesand the pressure nozzle was disposed coaxially within the air blast tubewith its discharge opening recessed of an inch from the dischargeopening of the air choke. In the first test of this example nocompressed air ring was utilized and no compressed air was charged tothe burner apparatus. In the second test of this example, a compressedair ring was utilized Upstream from and adjacent to the vaned air chokeand 95 cubic feet per hour of air compressed to a pressure of 1.25pounds per square inch was passed through the air ring and dischargeddirectly to the swirl vanes of the air choke. The results of the firsttest are shown in curve A of FIGURE 7 and the results of the second test-are shown in curve B of FIG- URE 7.

As shown in FIGURE 7, when utilizing a non-aspirating pressurizing oilspray nozzle, the use of a pressurized air ring advantageously increasedthe percentage of carbon dioxide in the flue gas from about 10.65 toalmost 13 at a smoke spot number of 1. While this improvement issubstantial, the improved results do not approach the 15.6 percent ofcarbon dioxide in the flue gas which would theoretically be achieved atcomplete combustion with stoichiometric air. Comparing the results ofthis example with the results of Example 1, it is seen that the bestresults by far are achievable when utilizing a swirling compressed airaspirating nozzle rather than a nonaspirating swirling pressurized oilnozzle.

Example Two tests were conducted to illustrate the etfect of thecompressed air ring in a burner apparatus utilizing an aspirating nozzleof the non-swirl type. The aspirating nozzle of this example is similarto the aspirating nozzles used in the previous tests except that themeans for swirling the pressurized air admitted to the nozzle wasremoved prior to the tests. Therefore, pressurized air admitted to thenozzle traveled through the nozzle with a non-swirling motion toaspirate fuel oil existing under atmospheric pressure. In the firsttest, 55 cubic feet per hour of air under a pressure of 5.7 pounds persquare inch Was passed through the nozzle in a non-swirling manner toaspirate 0.95 gallon per hour of fuel oil. An air choke having air swirlvanes reduced the discharge opening of the air blast tube from 4 inchesto 2 inches `and the discharge opening of the nozzle was recessed of aninch from the center of the discharge opening of the choke. Nocompressed air ring was utilized in the first test. In the second test,58 cubic feet per hour of air -unde' a pressure of 6.1 pounds per squareinch was passed through `the nozzle in a non-swirling manner. In thesecond test, a compressed air ring was disposed adjacent to and upstreamWith respect to the vaned air choke and 122. cubic feet per hour ofcompressed air under a pressure of 6.1 pounds per square inch was passedthrough the compressed air ring. A number of data points were obtainedin both the first and second tests by Varying the flow rate of air blownthrough the air blast tube. Referrng to FIGURE 8, the data obtained inthe first test, which was conducted without the compressed air ring, isndicated by the circular symbols, while the data obtained in the secondtest, which was conducted with the compressed air ring, is indieated bythe square symbols.

FIGURE 8 shows that when utilizing a non-swirl aspirating nozzle, noimprovement is obtained by utilizing a compressed air ring. In the testsof this example in which no compressed air ring was utilized the fluegases contained about 14 percent carbon dioxide at a smoke spot numberof 1, and this result was substantially unchanged when utilizing acompressed air ring. Therefore, while a compressed air ring functionscooperatively With an aspirating nozzle having means for swirling theaspirating air, it does not produce improved results when utilized withan aspirating nozzle which is devoid of aspirating air swirling means.

These results are explicable because nozzle swirling induces a highdegree of oil -atomization whereby the pressurized air passing throughthe compressed air ring is enabled to intifnately admix with the oil. Ahigh degree of oil atomization encourages rapid and completevaporization of individual oil droplets. It is only in the vapor stateth-at oil can admix with sufficent air to support its combustion. Oilvapor is highly combustble because it can freely admix with air whilelquid oil is not combustible because a liquid cannot admix withsufficient air to support combustion. Therefore, a liqud oil dropletonly burns at its surface where vaporization can occur, but the liquidnucleus of the droplet will not burn unless it can first v-aporize. Lackof swirling means in .a nozzle results in a very poorly atomized oilspray whereby the oil is unable to vaporize sufliciently rapidly toutilize the pressurized air passing through the compressed air ring,thereby rendering the compressed air ring innocuous.

Example 6 Further tests were conducted utilizing a swirling airaspirating nozzle which was designed to require about twice the amountof compressed air to aspirate a given Volume of fuel oil as was requiredby the swirling air aspirating nozzle of the tests of Example 1. In thetests of this example, the swirling air aspirating nozzle utilized 99cubic feet per hour of air at a pressure of 4.5 pounds per square inchto aspirate 0.81 gallon per hour of fuel oil under atmospheric pressure.This constitutes a ratio of compressed air to fuel oil of about 122cubic feet of compressed air per gallon of fuel oil. The first test ofthis example did not utilize a compressed air ring while the second testof this example utilized a compressed air ring adjacent to and upstreamwith respect to the vaned air choke and 81 cubic feet of air under apressure of 4.5 pounds per square inch was passed through the air ring.Except that a difierent nozzle was employed, the first test of thisexample utilized the apparatus of the test illustrated by curve A ofFIGURE 6 and the second test of this example utilized the apparatus ofthe test illustrated by curve B of FIGURE 6. A number of data pointswere obtained in both the first and second tests of this example byvarying the flow rate of air blown through the air blast tube. Theresults of the test of this example utilizing the compressed air ringare indicated by the square symbols in FIGURE 9 and the results of thetest of this example in which no air ring was employed are indicated bythe circular symbols in FIGURE 9.

As indicated in FIGURE 9, no improvement Was achieved by utilizing acompressed air ring, the percentage carbon dioxide in the fiue gas at asmoke spot number of 1 being about 15.2 both with and without an airring. The results shown in FIGURE 9 indicate that when a swirling airaspirating nozzle produces a spray having a high ratio of compressed airto fuel in the combustion apparatus, nearly optimum combustion isachieved. Therefore, the additional pressurized air discharged throughthe compressed air ring become innocuous.

Example 7 To further illustrate the criticality of the ratio ofcompressed air to fuel oil, the nozzle and apparatus of Example 6 wasemployed in two tests, each not utilizing a compressed air ring. In thefirst test, 92 cubic feet per hour of swirling air under a pressure of 4pounds per square inch Was passed through the nozzle and aspirated 1gallon per hour of fuel oil under atmospheric pressure from a level 1inch below the nozzle to produce a flue gas have 14.8 percent carbondioxide at a smoke spot number of 1. In the second test, the oil levelWas changed to require an oil lift of 5 inches rather than 1 inchwhereby 106 cubic feet per hour of swirling air under a pressure of 5pounds per square inch gauge was required to aspirate 1 gallon per hourof fuel oil. In the second test the fiue gas contained 15.4 percentcarbon dioxide at a smoke spot number of 1, which very closelyapproximates the optinum carbon dioXide percentage of 15.6,theoretically indicating complete combustion of the fuel oil with eX-actly stoichiometric air.

The showing of Example 7 is highly significant since it indicates thatan increase in the ratio of compressed air to fuel oil can be achievedwithout the utilization of a compressed air ring. Example 7 shows that adesired increase in the ratio of compressed air to fuel oil can beachieved by increasing the amount of compressed air required to aspiratea given quantity of fuel through the nozzle through the expedient ofincreasing the oil suction lift to the aspirating nozzle.

Various changes and modifications can be made without departing from thespirit of this invention or the scope thereof as defined in thefollowing claims.

We claim:

1. An apparatus for the combustior of fuel oil comprising an air blasttube having an air inlet end and an air discharge end, air blower meansfor blowing atmospheric air through said air blast tube from the inletend to the discharge end thereof, air choke means having air swirl vanesdisposed at the discharge end of said air blast tube, compressed airdelivery means near the periphery of said air blast tube Upstream fromsaid air choke means, said compressed air delivery means adapted todischarge compressed air toward said air swirl vanes, an aspiratingnozzle axially disposed in said air blast tube in the vicinity of saidair choke means, fuel oil supply means for supplying fuel oil undersubstantially atmospheric pressure to said aspirating nozzle, aircompressor means for supplying pressurized air to said aspirating nozzleand to said compressed air delivery means, air swirl means in saidaspirating nozzle for swirling the pressurized air supplied to saidaspirating nozzle, said aspirating nozzle adapted so that the swirlingmotion of pressurized air passing therethrough aspirates said fuel oiland discharges a swirling mixture of pressurized air and atomized oil,said air compressor means supplying a suflicient Volume of compressedair to said compressed air delivery means so that substantially completecombustion of the aspirated oil is achieved with only substantially astoichiometric quantity of air being supplied to said apparatus by saidair blower means and said air compressor means.

2. The combustion apparatus of claim 1 wherein said compressed airdelivery means is disposed within said air choke means.

3. The combustion apparatus of claim 1 wherein said compressed airdelivery means comprises a hollow ring extending along the periphery ofsaid blast tube having means for receiving compressed air and means fordischarging said compressed air in the direction of said air swirlvanes.

4. The combustion apparatus of claim 1 including means for adjusting theoutput of said air blower means and said compressed air delivery meansso that substantially a stoichiometric quantity of air is supplied tosaid apparatus by both said air blower means and said compressed airdelivery means.

5. The combustion apparatus of claim 1 including a disk having adiameter smaller than said air blast tube disposed in said air blasttube upstream from said nozzle.

References Cited UNITED STATES PATENTS 1,934,755 11/1933 Williams239-406 2,066,806 1/1937 Smith et al. 239-405 2,120,387 6/1938 Bargeboer239--406 2,181,527 11/1939 Vollmer 239-406 3,226,037 12/1965 Biber etal. 239-405 EVERETT W. K RBY, Primary Exam'ner.

1. AN APPARATUS FOR THE COMBUSTION OF FUEL OIL COMPRISING AN AIR BLASTTUBE HAVING AN AIR INLET END AND AN AIR DISCHARGE END, AIR BLOWER MEANSFOR BLOWING ATMOSPHERIC AIR THROUGH SAID AIR BLAST TUBE FROM THE INLETEND TO THE DISCHARGE END THEREOF, AIR CHOKE MEANS HAVING AIR SWIRL VANESDISPOSED AT THE DISCHARGE END OF SAID AIR BLAST TUBE, COMPRESSED AIRDELIVERY MEANS NEAR THE PERIPHERY OF SAID AIR BLAST TUBE UPSTREAM FROMSAID AIR CHOKE MEANS, SAID COMPRESSED AIR DELIVERY MEANS ADAPTED TODISCHARGE COMPRESSED AIR TOWARD SAID AIR SWIRL VANES, AN ASPIRATINGNOZZLE AXIALLY DISPOSED IN SAID AIR BLAST TUBE IN THE VICINITY OF SAIDAIR CHOKE MEANS, FUEL OIL SUPPLY MEANS FOR SUPPLYING FUEL OIL UNDERSUBSTANTIALLY ATMOSPHERIC PRESSURE TO SAID ASPIRATING NOZZLE, AIRCOMPRESSOR MEANS FOR SUPPLYING PRESSURIZED AIT TO SAID ASPIRATING NOZZLEANS TO SAID COMPRESSED AIR DELIVERY MEANS, AIR SWIRL MEANS IN SAIDASPIRATING NOZZLE FOR SWIRLING THE PRESSURIZED AIR SUPPLIED TO SAIDASPIRATING NOZZLE, SAID ASPIRATING NOZZLE ADAPTED SO THAT THE SWIRLINGMOTION OF PRESSURIZED AIR PASSING THERETHROUGH ASPIRATES SAID FUEL OILAND DISCHARGES A SWIRLING MIXTURE OF PRESSURIZED AIR AND ATOMIZED OIL,SAID AIR COMPRESSOR MEANS SUPPLYING A SUFFICIENT VOLUME OF COMPRESSEDAIR TO SAID COMPRESSED AIR DELIVERY MEANS SO THAT SUBSTANTIALLY COMPLETECOMBUSTION OF THE ASPIRATED OIL IS ACHIEVED WITH ONLY SUBSTANTIALLY ASTOICHIOMETRIC QUANTITY OF AIR BEING SUPPLIED TO SAID APPARATUS BY SAIDAIR BLOWER MEANS AND SAID AIR COMPRESSOR MEANS.